Disclosed is a method and apparatus for detecting machined substrate fragments within one or more internal chambers of a machined metal component, and more particularly, the use of non-destructive thermography for the detection of machined substrate fragments.
Non-destructive thermography for defect detection is generally known in the art. U.S. Pat. No. 4,996,426 discloses an apparatus for subsurface flaw detection of a continuously moving working piece, specifically, a rolled, worked metallic sheet. Heat is applied to a bottom surface of the workpiece causing thermal flow from the bottom to a top surface. Low thermal conductivity defects within the workpiece, including foreign material inclusions and subsurface cracks, cause thermal lines to flow around the defect creating low temperature areas on the top surface. An IR-detection device captures a thermal image of the top surface, wherein low temperature areas on the thermal image correlate with subsurface defects within the workpiece.
U.S. Pat. No. 8,581,975 and U.S. Pat. No. 5,834,661 disclose the detection of subsurface defects using thermography. U.S. Pat. No. 8,581,975 discloses a method and apparatus in which an induction coil applies heat to a powder-metallic component to cause a thermal increase flow through the body of the component and heat the component substantially uniformly throughout the component body. An IR-detection device creates a thermal image of the component following induction heating and subsurface inclusions, such as foreign metallic compounds, appear as different colors within the thermal image. U.S. Pat. No. 5,834,661 discloses a method wherein one side of a component is placed near a thermoplate and an opposing side is placed near a vacuum. As heat flows from the heated side to the vacuum side as the component cools, an IR-detection device captures a transient thermal image of the component. Subsurface inclusions appear as temperature/color variations within the transient thermal image.
Similarly, U.S. 2013/0261989 and U.S. Pat. No. 5,654,977 disclose methods of detecting subsurface defects at varying depths, such as foreign metal inclusions and subsurface laminations, using transient thermal imaging techniques.
The referenced apparatuses and methods detect defects such as foreign material and subsurface defects. Many of these disclosed apparatuses and methods detect subsurface defects. However, these disclosed methods and apparatuses, as well as others that are well known in the art, rely on a difference in material substance between the defect and the component substrate in order in order to effectively locate such defects using thermography techniques. In typical machining applications, machined substrate fragments, which fragments are composed of the same material substance as the component itself, are removed from the machined component body. These substrate fragments may be resident in one or more internal chambers of a machined component following a machining operation, which, if left undetected, can create component malfunctions following the installation and/or use of the machined component. It is an object of the disclosed method and apparatus to overcome these shortcomings in the art.